As functions loaded in a computer system configuring a storage system, for instance, a snapshot function and a journal function are known.
A snapshot function is a function for retaining an image of a certain logical volume at a certain point in time; for instance, at the time that a snapshot acquisition request is received from a host. As a result of periodically executing the snapshot function, a replication (i.e., backup) of data in the logical volume can be intermittently acquired. Moreover, the snapshot function can be used to restore a logical volume of the point in time that the snapshot was acquired.
A journal function is a function of creating, upon writing write data into a logical volume that is designated in a write command from a host computer, data (journal) containing such write data and control information concerning the writing of such write data, and storing the created journal.
Patent Document 1 discloses recovery processing to be executed at a point in time other than the point in time that a snapshot was created by writing write data in a journal into the snapshot that was acquired with the snapshot function. In Patent Document 1, by giving consideration to the fact that the journal volume will become full if the acquisition of journals is repeated and subsequent data recovery will become impossible, if the unused amount of the journal volume falls below a threshold limit, the snapshot is updated by applying a journal entry to the snapshot so as to increase the unused capacity in the journal volume.
Patent Document 2 discloses the switching of a snapshot and a journal. In Patent Document 2, if it becomes difficult to secure the time length for backup, the mode is switched from a snapshot mode to a journal mode for effectively performing backup and restoration.
Patent Document 3 discloses the operation of a snapshot restoration volume. In Patent Document 3, during the restoration processing, since only update differential data is copied from the differential volume to the operation volume, it is possible to reduce the amount of data to be transferred, and consequently reduce the load of the storage apparatus during the restoration processing.